Laminated paper



March 14, 1961 w. E. ANDERSON LAMINATED PAPER Filed Feb. 18, 1957 N @E m INVENTOR WILLIAM E. ANDERSON BY United States Patent LAMINATED PAPER William E. Anderson, Bloomsbury, N.J., assignor to Riegel Paper Corporation, New York, N .Y., a corporation of Delaware Filed Feb. 18, 1957, Ser. No. 640,725

2 Claims. (Cl. 154-138) This invention relates to laminated paper and, more particularly, to a moisture-proof lamination of two sheets of paper held together by a thin film of parafin. The invention further provides an improved method for manufacturing a paraifin-coated laminated paper, in which only one surface of the lamination is coated with the protective layer of paraffin.

The use of automatic high-speed packaging machines to wrap food products has been accompanied by the development of specially-coated papers to meet the individual packaging requirements of each commodity. A suitably coated paper for wrapping powdered gelatin, for example, not only must be moisture-proof to prevent caking of the powder, but preferably should be sealed by compression alone since heat sealing tends to impair the gelling properties of the powder enclosed within the package. Such a paper should also possess sufficient strength for use in automatic packaging machinery, yet not be so heavy as to appreciably increase the freight costs in shipping the packaged product.

Although paraffiin coated papers have been extensively used to package powdered gelatin, the commercially available parafiln coated papers generally are difficult to use in automatic packaging machinery. For the most part, these papers consist of a heavy sheet coated on both sides with paraflin. Yet certain packaging machinery require that one surface be substantially free of wax.

Using a lamination of two thin sheets of paper, I have developed a moisture-proof packaging paper which may be sealed by compression and which is especially suited for use in automatic packaging machinery. The packaging paper of the invention comprises a lamination of two sheets of paper held together by a thin film of parafiin. Only one surface of this lamination is coated with a thin layer of paraffin for the remaining surface is uncoated.

By using unilaterally unglazed sheets of paper to form the lamination, the uncoated surface of the lamination can be formed from the unglazed side of one of the sheets. Such laminations, having one surface unglazed and the other coated With a parafiin layer, have been found to be less prone to curl when used in automatic packaging machinery.

In manufacturing the laminated paper of the invention, a continuous sheet of paper is completely immersed in a bath of molten paraflin, and upon emergence from the bath the coated sheet is immediately laminated to a second uncoated sheet of paper. In this manner, the lamination of the two sheets is held together by a thin layer of paraffin, and only one surface of the lamination is coated with a paraffin layer.

To obtain an unglazed surface on the uncoated side of the lamination, and thus diminish the tendency of the finished product to curl, the parafiin coated sheet emerging from the bath is laminated to a unilaterally unglazed sheet of paper so that the unglazed side forms the uncoated surface of the laminate.

Although various types of paper may be used in manu- 2,975,094 Patented Mar. 14,. 1961 facturing the laminated paper of the invention, I have found that laminations made from a standard sulphitebleached paper, weighing from 18 to 20 pounds per ream, may be employed in any packaging machinery using compression sealing. One especially suitable type of paper used to manufacture the lamination contained 70 percent by weight of southern full bleach kraft and 30 percent by weight of Canadian sulphite-bleached softwood. Other papers successfully employed contained larger quantities of Canadian sulphite-bleached softwood, and some papers made from a hardwood pulp have also been found satisfactory.

Selection of the paraffin coating is limited to parafiin waxes melting in the temperature range of from 131" 'to 145 F. and advantageously 133 to F. These paraffins, which may be modified by the inclusion of microcrystalline Waxes or butyl rubber, can be sealed by compression only. Other parafiin waxes melting from 123 to 126 F. for example have too high an oil content and cause blocking or sticking together of the laminated paper roll stock in the summer months. Paraflin waxes with melting points above the F. range usually crack and flake on the packaging machine when they are folded which allows the flake of paraffin to accumulate on the machine and drop into the product and contaminate it.

An illustrative embodiment of the invention is described below with reference to the accompanying drawing in which:

Fig. 1 is a schematic elevation of apparatus used to manufacture laminated paper in accordance with the process of the invention, and

Fig. 2 is a cross-sectional view of the laminated paper.

Referring to Fig. 1 of the drawing, the laminated paper may be manufactured from two separate rolls of paper which are unwound into sheets 3 and 4. These sheets of paper are preferably unglazed on one surface to give less curl in the finished laminated paper, and are made on a standard paper making machine with only one side engaging the dryer rolls. Various types of paper may be successfully employed, but a sulphite-bleached paper weighing between 18 to 20 pounds per ream (500 sheets- 24 x 36") has been found to be preferable.

The sheets 3 and 4 are brought together so that the glazed surface of each sheet is face-to-face with the glazed surface of the other. This may be accomplished in any suitable manner. I

In this position, with the glazed surfaces of each sheet face-to-face, the two sheets are passed about a heated roller 7 with sheet 4 innermost. It is essential to pass both sheets over the heated roller 7 in order to equalize the moisture contents of both sheets. If, for example, only one sheet was heated it would lose moisture and thus shrink. On laminating this sheet with lower moisture content to another sheet with higher moisture content, the laminated web will curl as the low moisture content sheet picks up or regains its lost moisture and begins to expand.

After the two sheets 3 and 4 have passed around the heated roller 7, the sheet 4 innermost to the roller is immersed in a bath 8 of molten paraflin wax. Entering the bath 8 of parafiin, the sheet 4 passes around two retaining rollers 9 and 10 submerged in the paratfin bath. As indicated previously, only paraflin melting in the range from 131 to 145 F. (preferably from 133 to 135 F.) may be used, since laminations made from higher and lower melting waxes cannot be employed for the reasons set forth hereinabove. However, the paraflin waves used may be modified by the inclusion of microcrystalline waxes or small amounts of butyl rubber. Sufficient wax is employed so that in the finished product there are about from 16 lbs. to 20 lbs. (advantageously about 18 lbs.) per ream.

Upon emerging from the bath 8 of molten paraffin, the coated sheet 4 re-joins the uncoated sheet 3, and both sheets are passed through laminating rolls 11 and 12.

The resultant lamination, as shown in Fig. 2, consists of the two sheets 3 and 4 held together by a thin film of paraffin 13. One surface of the lamination is coated with a layer of paraffin 14, while the remaining surface is unglazed, since it is formed by the unglazed surface of sheet 3.

This laminated paper has been employed successfully in substantial quantity in automatic packaging machinery using compression sealing, and requires no heat sealing to form a moisture-proof package.

I claim:

1. A moisture-proof packaging paper comprising a lamination of two sheets of unilaterally-unglazed sulphitebleached paper, a thin film of paraffin between said sheets and in contact with the glazed surfaces thereof, and a thin layer of parafiin covering one of the exposed, un-

References Cited in the file of this patent UNITED STATES PATENTS 1,965,719 Nelson July 10, 1934 2,171,775 Wilshire Sept. 5, 1939 2,256,916 Wilshire Sept. 23, 1941 2,783,183 Ferris Feb. 26, 1957 OTHER REFERENCES Dean: Paper Trade Journal, vol. 120, No. 7, Feb. 15, 1945 (pages 28-32). 

1. A MOISTURE-PROOF PACKAGING PAPER COMPRISING A LAMINATION OF TWO SHEETS OF UNILATERALLY-UNGLAZED SULPHITEBLEACHED PAPER, A THIN FILM OF PARAFFIN BETWEEN SAID SHEETS AND IN CONTACT WITH THE GLAZED SURFACES THEREOF, AND A THIN LAYER OF PARAFFIN COVERING ONE OF THE EXPOSED, UNGLAZED SURFACES OF THE LAMINATE, SAID PARAFFIN HAVING A MELTING POINT BETWEEN 131*F. AND 145*F. 